Spark ignition apparatus for internal combustion engines



Nov. 11, 1969 N. A. JUKES 3,478,249

SPARK IGNITION APPARATUS FOR INTERNAL COMBUSTION ENGINES Filed Feb. 2,1967 FT Z PRIOR ART PRIOR ART United States Patent US. Cl. 315-209 6Claims ABSTRACT OF THE DISCLOSURE The spark ignition apparatus comprisesa spark generating circuit for supplying sparks to the plugs of theengine in turn, a trigger circuit which when biased by an input permitsthe spark generating circuit to produce a spark, a continuously runningoscillator for providing the biasing input to the trigger circuit, andmagnetic means driven by the engine for coupling the oscillator to thetrigger circuit when a spark is required, the design of the triggercircuit being such that irrespective of engine speed only one spark isproduced each time the oscillator is coupled to the trigger circuit.

This invention relates to spark ignition apparatus for internalcombustion engine-s.

This invention has for an object to provide spark ignition apparatuscomprising a spark generating circuit for supplying sparks to the plugsof the engine in turn, a trigger circuit which when biased by an inputpermits the spark generating circuit to produce a spark, a continuouslyrunning oscillator for providing the biasing input to the triggercircuit, and magnetic means driven by the engine for coupling theoscillator to the trigger circuit when a spark is required, and in whichthe design of the trigger circuit is such that irrespective of enginespeed only one, i.e., a single spark is produced each time theoscillator is coupled to the trigger circuit.

It is a further object of the invention to provide spark ignitionapparatus as set forth in the foregoing object, and in which the triggercircuit includes a feed-back path which accelerates the switching actionand is useful particularly at low speeds to assure the emission of suchsingle spark.

Further and more specific objects will be apparent from the accompanyingdrawings, in which:

FIGURE 1 is a circuit diagram illustrating an embodiment of theinvention, and

FIGURES 2 and 3 are, respectively, diagrammatic side and frontelevational views of a form of magnetic coupling arrangement for use inthe circuit of FIGURE 1.

Referring to the drawings, there are provided a positive supply line 11which in use is connected to the positive terminal of the battery of thevehicle through an ignition switch 12, and a negative line 13 whichconveniently is earthed. Connected between the lines 11, 13 are a freerunning oscillator, a trigger circuit, and a spark generating circuit.

The oscillator includes a capacitor 14 connected between the lines 11,13 in parallel with a series circuit including a resistor 15 and acapacitor 16. A point inter mediate the resistor 15 and capacitor 16 isconnected through the secondary winding 17 of a transformer 18 to thebase of an n-p-n transistor 19, the collector of which is connected tothe line 11. The emitter of the transistor 19 is connected to one end ofa resistor 21, the other end of which is connected to the line 13through the primary winding 22 of the transformer 18 and a capacitor 23in parallel, and is also connected to an output terminal 24.

The trigger circuit is in the form of an amplifier with AC. feed back,and includes a resistor 25, one end of which is connected to the line 11and the other end of which is connected to the base of an n-p-ntransistor 26, and to the collector of an n-p-n transistor 27. Thetransistor 26 has its collector connected to the line 11 through aresistor 28, and its emitter connected to the line 13 through a resistor29, while the transistor 27 has its emitter connected to the line 13,and its base connected to the line 13 through a resistor 31. The base ofthe transistor 27 is further connected to the line 13 through a diode 32and the capacitor 33 in series, and a point intermediate the diode 32and capacitor 33 is connected to an input terminal 34. The AC. feed backis provided by way of a resistor 35 and a capacitor 36 connected inseries between the collector of the transistor 26 and the base of thetransistor 27.

The spark generating circuit includes an ignition coil 37 having asecondary winding 38 which is connected to the spark plugs of the enginein turn through a distributor in the usual way, and a primary winding 39one end of which is connected to the line 11, and the other end of whichis connected to the collector of an n-p-n transistor 41, the emitter ofwhich is connected to the line 13, and the collector and emitter ofwhich are bridged by a voltage-dependent resistor 42. The sparkgenerating circuit is coupled to the trigger circuit by way of aconnection from the base of the transistor 41 to the emitter of thetransistor 26. There is further provided magnetic means for coupling theoscillator to the trigger circuit at the instant when a spark isrequired. This magnetic means includes an output coil 43 connectedbetween the terminal 24 and the line 13, and a pick-up coil 44 connectedbetween the terminal 34 and the line 13. The pick-up coil 44 is tuned tothe operating frequency of the oscillator. The magnetic means ispreferably contained within the distributor of the road vehicle, and maybe of the form illustrated in United States Patent No. 3,277,340 whichis described briefly herein in connection with FIGS. 2 and 3. Themagnetic circuit for coils 43 and 44 comprises an open rectangular core49 which is split along one of its long sides. The windings 43 and 44are wound on the limbs or opposite sides of the split in the core, andthe arrangement is such that the air gap between the windings issufficient for magnetic coupling. Rotatable about an axis parallel toone of the longer sides of the core is a disc 51 which is driven by, andat a speed dependent on, the speed of the engine with which the ignitioncircuit is associated. Thus, conveniently the disc 51 may be driven bythe distributor shaft diagrammatically shown at 53.

The disc is made of conductive material and includes four slo s 51 whichextend inwardly towards the center of the disc from its circumferenceand which are mutually at right angles. The disc is rotated so that itpasses between the windings or coils 43 and 44, and when a slot 52 isaligned with the two portions of the broken limb on which windings 43and 44 are wound, the windings are coupled magnetically. The windingsare not coupled at any oher time. The disc described is suitable for usewith a four cylinder engine, and in other cases the number of slots willbe equal to the number of cylinders, Moreover, the disc 51 could bedriven indirectly by the engine through step-up or step-down gearing, inwhich case the number of slots could be a fraction of or a multiple of,the number of engine cylinders.

In use, between the production of sparks, current flows through theresistor 25 to switch the transistor 26 on, and the transistor 26 inturn switches on the transistor 41, so that current flows in the primarywinding 39. The

oscillator operates in known manner, and in a typical case may have afrequency of 600 kilocycles per second.

At the instant when a spark is required, the windings 43, 44 are coupledmagnetically, and the output from the oscillator is rectified by thediode 32 and fed to the base of the transistor 27, so turning thetransistor 27 on. The base current supplied to the transistor 26 nowfiows through the transistor 27 instead, and so the transistor 26 isturned off, with consequent turning off of the transistor 41. Theresultant fall in flux in the ignition coil 37 produces the spark.

While the transistor 27 is switching on and the transistors 26, 41 areswitching off, the voltage at the collector of the transistor 26 rises,so that the capacitor 36 is charged by way of the resistor 35. This feedback signal accelerates the switching action, so that the rate of fallof collector current in the transistor 41 is less dependent on the rateof rise of the current in the winding 44,

It -will be appreciated that the transistor 27 is held off until asignal of sufficieut amplitude appears at the terminal 34. Because ofthe design of the circuit, only one spark will be applied to a plug eachtime the windings 43, 44 are coupled, and by virtue of this arrangementthe design of apparatus for use with engines having a large number ofcylinders, for example, in excess of six, is considerably simplified ascompared with arrangements in which at speeds below a predeterminedengine speed each plug may have more than one spark applied thereto eachtime the windings 43, 44 are coupled.

In practice, it is convenient to house the oscillator, the triggercircuit and the transistor 41 and resistor 42 in the same container, andthis container can be the distributor. In this case, the distributor isdesigned to act as a heat sink for the transistor 41.

The purpose of the resistor 21 is to provide negative feed back withinthe oscillator, which assists in stabilizing the frequency of theoscillator against changes in the supply voltage. The capacitor 16provides a low impedance path in the feed back circuit of theoscillator, and the resistor 15 is provided to ensure that theoscillator starts satisfactorily.

The voltage dependent resistor 42 prevents damage to the transistor 41as a result of the back when the flux in the ignition coil 37 collapses,and also prevents damage as a result of transient Volta-gm reflectedfrom the windings 38 during production of a spark. The resistor 29 alsoprotects the transistor 41 when the spark is produced.

It should now be appreciated that among the important features of theinvention is the ability to tune the oscillator into resonance with theoutput winding of the pick-up coil, as well as the provision of the AC.positive feed back for the A.C. amplifier connection of transistors toinsure the desired operation at low speeds. Also, the use of the voltagedependent resistance enables the suppression of transients at thecollector of transistor 41.

Thus, it will be appreciated that the characteristics and features ofthe principle of the invention enable the positive control of theproduction of a single spark for each cylinder to be fired. From areading of the description hereof other and further modifications mayoccur to those skilled in the art and accordingly it is intended thatthe invention be limited only by the scope of the appended claims.

What is claimed is:

1. Spark ignition apparatus for an internal combustion engine,comprising a spark generating circuit for supplying a single spark toeach of the plugs of the engine in turn, a trigger circuit connected tosaid spark generating circuit comprising a first transistor and a secondtransistor interconnected for mutually exclusive operation and whichcircuit is normally in one condition of operation but when biased by aninput assumes a second condition of operation to cause the sparkgenerating circuit to produce a single spark, a continuously operatingfixed frequency oscillator for providing the biasing input to saidtrigger circuit, magnetic means driven by the engine for coupling saidoscillator to said trigger circuit when a spark is required to drivesaid trigger circuit from said one condition to said second condition,said trigger circuit remaining in said second condition until saidtrigger circuit is decoupled from said oscillator, and a feedbackcircuit from the second transistor to the first transistor to acceleratethe switching action from said first condition of operation to saidsecond condition of operation.

2. The apparatus of claim 1 wherein said transistors of the triggercircuit are connected in DC. amplifier fashion and said feed backcircuit comprises a positive feed back circuit.

3. The apparatus of claim 1 wherein said spark generating circuitcomprises a transistor connected to be operated simultaneously with thesecond transistor; and further comprising a voltage dependent resistanceconnected between the emitter and collector electrodes of the sparkgenerating circuit transistor.

4. The apparatus of claim 1 comprising pick-up coil means fortransferring energy from the oscillator to the first transistor; saidpick-up coil means being tuned to resonance with the oscillator.

5. The apparatus of claim 1 further comprising rectifying meansinterposed between the oscillator and the transistors to permit thelatter to operate in DC amplifier fashion.

6. Spark ignition apparatus for an internal combustion engine of thespark plug type, comprising a spark generating circuit forintermittently supplying a single spark for each explosion, said sparkgenerating circuit comprising a spark generating transistor, a triggercircuit comprising a first transistor and a second transistor connectedin circuit and to the spark generating transistor, said trigger circuitnormally characterised by conduction of said second transistor andnon-conduction-of said first transistor but when biased by inputshifting conduction from the second transistor to the first transistorwith the second transistor and spark generating transistor becomingnon-conductive to generate a spark, a continuously operable oscillatorfor providing the bias input, pick-up winding 'means tuned to thefrequency of said oscillator, and magnetic means driven by the enginefor coupling said oscillator to said trigger circuit via said windingmeans each time a spark is required for explosion, said trigger circuitreturning to conduction in said second transistor and non-conduction insaid first transistor when said trigger circuit is decoupled from saidoscillator, and said trigger circuit including a positive feedback pathbetween the second transistor and the first transistor for increasingthe speed at which the first trausistor becomes conductive when thetrigger circuit is coupled to the oscillator.

References Cited UNITED STATES PATENTS 3,161,803 12/1964 Knittweis315-209 3,240,199 3/1966 Neopolitokis 123-448 3,277,340 10/1966 Iukes eta1. 3l5214 3,291,110 12/1966 Peters 123l48 3,299,874 1/1967 Elkind123148 JOHN W. HUCKERT, Primary Examiner SIMON BRODER, AssistantExaminer US. Cl. X.R. 3l5218

